Optical navigation systems, which are commonly found in optical computer mice, have traditionally used light-emitting diodes (LEDs) as light sources. Recently, however, optical navigation systems that use lasers as light sources have been developed. The laser-based optical navigation systems are more sensitive to surface features than the LED-based optical navigation systems. Thus, laser-based optical navigation systems are able to accurately track on more challenging surfaces such as polished surfaces.
Most lasers are capable of causing eye injury, even permanent eye damage, to users who look directly into the laser beam. The severity of the eye injury depends on the power of the laser beam. Thus, laser-based optical navigation systems require a much more stringent eye safety regulation than the LED-based optical navigations systems. IEC 60825-1 standard is applicable to safety of laser products including laser optical mice. In order for a laser optical mouse to be classified as Class-1 product (eye-safe under all operating conditions) under the IEC 60825-1 standard, the maximum optical power output of the laser source of the laser optical mouse must not exceed a prescribed threshold, which is dependent on the wavelength and its mode of operation. As an example, a single mode vertical-cavity surface-emitting laser (VCSEL) with a nominal wavelength of 840 nm must have a peak output power of less than 716 uW in the Continuous Wave (CW) mode to be classified as Class-1 product.
Current laser-based optical navigation systems are open loop systems. Thus, to produce Class-1 laser optical mice, every laser needs to be tested to determine the threshold current, the slope efficiency and the temperature coefficient. Each laser is then matched with a fixed binning resistor in the current regulating circuit. The drive current for each laser is adjusted through sensor digital-to-analog converter (DAC) bits so that the power of the laser is set at a fixed value, e.g., 500 uW.
A concern with these conventional laser-based optical navigation systems is that the calibration process of the lasers is very tedious, time consuming and costly, and may result in low manufacturing productivity. Another concern is that customers will need to control their manufacturing environment, especially temperature, to ensure that the initial calibration parameters are maintained within acceptable ranges.
Thus, there is a need for a laser-based optical navigation system that addresses the above-described concerns.